T-Mobile USA, the nation’s fourth-largest carrier and the sole major U.S. telco without Apple’s iPhone, announced at the GigaOm Mobilize conference that it will be rolling out its iPhone-compatible HSPA+ network in Las Vegas on Monday, September 24, 2012.

The carrier’s HSPA+ network runs in the much more common 1900MHz spectrum, allowing unlocked iPhone owners to finally access the fastest 3G network in the country, T-Mobile’s dual-carrier HSPA+…

According to GigaOM, the spectrum refarming process is now 75 percent complete in Las Vegas. T-Mobile CTO Neville Ray said at the conference that a material portion of the carrier’s network will be iPhone-ready by the end of 2012. Seattle, Washington, DC and the New York metro area will also get T-Mobile’s HSPA+ by year’s end.

T-Mobile’s dual-carrier HSPA+ network doubles the 21Mbps download peak of HSPA+ radio technology to a theoretical maximum of 42 Mbps.

As you can see on Apple’s Compare iPhones page, the new iPhone 5 supports dual-carrier HSDPA (the fastest 3G radio technology), in addition to HSPA+, CDMA EV-DO Rev. A and Rev. B and the fastest 4G LTE. In comparison, the iPhone 4/4S tops out at HSPA data speeds of 14.4Mbps.

Despite advertising against Apple, T-Mobile is happy to host more than a million owners of unlocked iPhones on its network who only get to use the slower 2G EDGE connection because T-Mobile’s AWS frequency band operates at less common frequency ranges not supported by Apple’s device.

Only customers covered by T-Mobile’s HSPA+ 1900MHz network are able to use their iPhone to download data at 3G speeds. Yes, T-Mobile’s HSPA+ is technically souped up 3G technology though it’s been hailing its network as “4G”, which is simply deceptive advertising.

PCWorld tests show that an iPhone 4S running on T-Mobile’s HSPA+ network on the 1900MHz band is on average average more than two times faster than AT&T’s 3G network (5.53 Mbps vs. 2.62 Mbps).